The original goals of this project were the isolation of a rat thyroid hormone receptor cDNA in order to study the structure and function of the thyroid hormone receptor. The methodology as initially proposed involved the development of an anti-thyroid hormone receptor antibody for isolation of a rat thyroid hormone receptor cDNA from a cDNA library by epitope selection. New information has become available indicating that the cellular homolog of the avian erythroblastosis virus (v-erb-A) gene, c-erb- A, encodes a thyroid hormone receptor. By using synthetic peptides from the putative ligand-binding and DNA-binding domains of v-erb- A, a polyclonal anti-rat thyroid hormone receptor antibody has been developed. By using a v-erb-A hybridization probe, isolation of a rat thyroid hormone receptor cDNA(s) from a rat brain cDNA library has been carried through to the tertiary screening phase. In the next two years it is anticipated that the translation products of v-erb-A and c-erb-A (thyroid hormone receptor) will be studied in vitro in order to characterize their ligand-binding and DNA-binding properties. Transfection studies with both v-erb-A and c-erb-A are planned to document the functional expression of the translation products. Transient expression studies have been designed which will define the role of the v-erb-A and c-erb-A products in activating the thyroid hormone responsive promotor from the rat growth hormone gene, in transfected cells. A panel of variant receptor proteins will be generated by deletion/insertion mutagenesis and site-directed mutagenesis to more fully explore the structure/function relationship of thyroid hormone receptor.